The present invention pertains to a magenta ink for inkjet printing and, in particular, to a magenta ink comprising a certain combination of magenta colorants. The present invention further pertains to an ink set comprising this magenta ink and a certain cyan and yellow ink. The ink and ink set provide advantageous color and light-fastness.
Inkjet printing is a non-impact printing process in which droplets of ink are deposited on a substrate, such as paper, to form the desired image. The droplets are ejected from a printhead in response to electrical signals generated by a microprocessor. Inkjet printers offer low cost, high quality printing and have become a popular alternative to other types of printers.
Inkjet printers are equipped with an ink set which, for full color printing, typically comprises a cyan, magenta and yellow ink (CMY). An ink set will also commonly comprise a black ink (CMYK). Colorants for the inks can be soluble in the ink vehicle (dyes) or insoluble (pigments).
The ink set should provide printed images having good color characteristics, such as correct hue and high chroma. Preferably, the ink set will achieve these favorable characteristics on a range of media including plain paper as well as specialty media such as transparency film and coated paper. Also, preferably, the hard copy output is reasonably light-fast.
A suitable ink should generally exhibit good crusting resistance, good stability, proper viscosity, proper surface tension, good color-to-color bleed alleviation, rapid dry time, consumer-safety and low strike-through.
Various magenta, yellow and cyan dyes, and CYM dye sets, have been disclosed for plain paper and photo paper printing. Most of the attention though is directed to selection of the magenta colorant as it tends to be the colorant most vulnerable to light fade. It is desirable for a dye to have the best possible light-fastness.
Reactive Red 180 is probably the most commonly mentioned magenta dye for use in inkjet inks. It can be used alone or in combination with Acid Red 52 to achieve a more violet shade. However, U.S. Pat. No. 6,641,257, provides light-fastness evaluation of a number of magenta dyes and Acid Red 37, Acid Red 289, Direct Red 75, Direct Red 212, Reactive Red 141, Reactive Red 23 and Reactive Red 195 are all more light-fast than Reactive Red 180.
A magenta ink with excellent light-fastness comprising a mixture of Magenta 377 and Acid 52 is disclosed in U.S. Pat. No. 5,772,742. Ink comprising hydrolyzed Reactive Red 23 magenta colorant is disclosed in U.S. Pat. No. 6,458,195 as having high lightfastness. Magenta inks comprising certain copper complex azo dyes are disclosed in U.S. Pat. No. 6,521,032 as having good color and light-fastness.
Other known dyes for magenta inkjet inks include Direct Red 227 as disclosed, for example, in U.S. Pat. No. 5,143,547 as part of a CYM ink set. A mixture of magenta anthrapyridone dye and Reactive Red 23, Reactive Red 24, Reactive Red 31, Reactive Red 120, Reactive Red 180, Reactive Red 241, Acid Red 35, Acid Red 52, Acid Red 249, Acid Red 289, Acid Red 388, Direct Red 227 or CAS No. 153204-88-7 is disclosed in U.S. Pat. No. 6,706,102. A mixture of Acid Red 92 and Reactive Red 180, Direct Red 75, or Reactive Red 159 is disclosed in U.S. Pat. No. 6,793,722.
Dye-based cyan ink with good light-fastness is disclosed in U.S. Pat. No. 6,379,441. Dye-based yellow inkjet inks comprising Acid Yellow 79 and either one or both of Direct Yellow 169 and Acid Orange 33 are disclosed in co-owned and co-pending application U.S. App. Ser. No. 60/993,373 (filed Sep. 12, 2007).
Sets of dye-based inkjet inks having good color and light-fastness are disclosed in U.S. Pat. Nos. 5,749,951; 5,851,273; 5,858,075; 6,183,548, and 6,712,462.
Still, a need exists for improved inks and ink sets that provide vivid color and fade resistance, especially on specialty paper such as photo-glossy paper.